Protecting coating



Patented May 13,1941

2.2413593 rao'rno'rmc COATING Heinrich van Thiel, Leuna, Germany, assignor, b mesne assignments, to Walter H; Duisberg,

New York, N. Y.

No Drawing. Application November 24, 1937, Se-

rial No. 176,314. In Germany November 27,

4 Claims.

The present invention relates to a process of protecting the internal surfaces of containers for liquid fuels.

When storing liquid fuels, such as benzine, benzene, methanol and the like, the choice of material for the containers or reservoirs offers considerable difilculty because the liquid fuels frequently contain constituents which attack ordinary iron and many other materials. The use of alloy steel is, however, not feasible for economical reasons, in particular in large plants.

It has already been proposed to protect the inner surfaces of iron reservoirs from corrosion by coating them with organic binding agents, such as resins, bitumen or rubber, or by sticking on foils of other metals. None of these methods has hitherto proved successful. Furthermore it is impossible to construct such reservoirs of concrete because the problem of rendering the concrete mass effectively impermeable to light benzines, benzene, methanol or the like has not hitherto been satisfactorily solved.

I have now found that ordinary iron may be directly used as constructional material for reservoirs, pipes and other apparatus coming into contact with liquid fuels by applying to the internal surfaces thereof a coating of cement, allowing the latter to harden in an atmosphere saturated with water vapor and then, after sufficient setting, subjecting it to a fiuation. In the latter process, which is known for the hardening of concrete surfaces, the amount of free calcium oxide contained in the concrete surface is converted into insoluble fluorides by salts-of fluosilicic acid. Before the application of the protective coating to the surface to be protected, the latter should be thoroughly freed from rust, preferably by means of a sand-blast.

The most favorable temperature to "be maintained during the application of the coating mass lies between about and about C. In summer it is therefore often preferable to cool the container by external trickling, whereas in the case of frost an internal heating of the container is necessary; any formation of ice in the coating should be avoided in all cases.

For the production of a good coating it is important that the coating should not dry out during setting; such nonpermissible drying out may frequently be recognized by a change in color of the applied layer. An atmosphere saturated with water vapor is therefore maintained in the inner space of the parts of theplant to be coated. It is preferable to apply the cement coating in v i at least two working operations, whereby after each working operation the setting ofthe layer just applied must be awaited before the next layer is applied. After repeatingthe-application f of the coating one or more times, the total thickness of the whole. layer advantageously not exceeding about 2 millimeters, the finished coating is subjected to the fluation. I l

By the said measures there is obtaineda coating which has a different permeability for benzine, benzene, methanol and the like on the one hand and for the corrosive constituents on the other hand. It keeps back the corrosive constituents without being itself attacked by them. While hitherto iron containers, such as it was necessary to use in default of another economical constructional material, had only a very limited life and after emptying it was necessary each time to remove therefrom by troublesome and dangerous operations the corrosion products which would lead to soiling of the stored fuel, the iron fuel reservoirs provided with the said protectivecoating have a practically unlimited life without undesirable corrosion taking place.

In addition to the economical advantages thus obtained there is' also the advantage that any soiling of the fuel by corrosion products from the container is avoided with certainty.

The said method of working may be applied in a similar manner to all containers, tubular conduits, pipes and other apparatus coming into contact with liquid fuels, including those constructed of materials other than iron. It is presupposecl that the apparatus are not subjected to any considerable elastic deformation during use. The application of the protective coating to the interior of tubular conduits or pipes is preferably effected by centrifugal processes.

In order to shorten the time of hardening, for example in containers which are suitable for the reception of high pressures, the known vapor,

hardening processes under vapor pressure may also be used.

The following example will further illustrate the nature of this invention but the invention is not restricted to this example. The parts are by weight.

Example A tank intended for thestorage of benzine is freed from rust by means of a sand-blast and then provided with a coating of cement prepared parts of water. After hardening for three days in an atmosphere saturated with water vapor at an external temperature of 20 0., there is applied to the coating which is 0.5 millimeter thick a second coating which is allowed to harden for another seven days in an atmosphere saturated with water. vapor. The coating is then treated with a dilute solution of a magnesium salt of fluosilicic acid. The tank provided-with the said coating, which is 1.0 millimeter in thickness in all, shows no trace of corrosive attack after use for several years.

A container prepared in the same way and used for the storage of methanol also shows the same resistance to corrosion.

What I claim is:

1. The process of protecting the internal surfaces of iron containers and tubes for liquid fuels which comprises applying to the said surfaces a coating of hydraulic cement at most about 2 millimeters in thickness, allowing the latter to harden at temperatures of about 20 C. in an atmosphere saturated with water vapor and then, after setting, subjecting it to a treatment with a soluble salt of fiuosilicic acid which forms insoluble fluorides with the coating substance.

2. The process of protecting the internal surfaces of iron containers and tubes for, liquid fuels which comprises applying to the said surl faces a coating of hydraulic cement at most about 2 millimeters in thickness, allowing the latter to harden at temperatures otabout 20 C. in an atmosphere saturated with water vapor and then, after setting, subjecting it toa treatment with an aqueous solution of magnesium fluosilicate.

3. In the process as claimed in claim 1 repeating at least once the step of applying a coating of hydraulic cement before treating the surface with a salt of fluosilicic acid the total thickness of the cement layers being at most about 2 millimeters.

4. The process of protecting the internal surfaces of iron containers and tubes for liquid fuels which comprises applying to said surfaces a. coating of hydraulic cement at most about 2 millimeters in thickness at a temperature of between about 10 and 20 0., allowing the latter to harden at temperatures of about 20 C. in an atmosphere saturated with water vapor, and then, after setting, subjecting it to a treatment with a soluble salt of fiuosilicic acid which forms insoluble fluorides with the coating substance.

HEINRICH VAN TI-IIEL. 

